Embodiments of the present invention relate generally to imaging techniques and more particularly to computed tomography (CT) systems and methods for improving image resolution.
Cardiac imaging is a critical function in clinical applications. Characterization of myocardial motion enables better understanding of the physiology of a heart and early detection of cardiovascular diseases. Particularly, cardiologists employ CT angiography (CTA) images to diagnose and characterize the extent of heart disease. Imaging the heart, however, is particularly challenging, as the heart is a moving object that rotates, translates and deforms non-rigidly in a three-dimensional (3D) space. Conventional CT image reconstruction methods generally assume that an object is stationary during data acquisition. In cardiac imaging, application of the conventional reconstruction methods may result in image blurring and other motion artifacts in the reconstructed images due to heart motion. The artifacts can severely affect a diagnosis that uses these reconstructed images, especially if the imaged features are small. For example, plaques formed in coronary arteries are generally indicative of a risk of a potential heart attack, but are difficult to image due to their small size. Non-optimal reconstruction of such small features may result in incorrect diagnosis resulting in serious consequences. Therefore, an ability to produce high-resolution images is critical to clinical diagnosis.
Conventional imaging techniques employ brute force approaches to mitigate effects of motion artifacts in CT imaging. Some of these techniques include employing two X-ray tubes or detector pairs angularly offset from each other, a heavier or higher power tube combined with spinning a gantry faster, or combining data from successive heart cycles. These techniques, however, incur considerable costs, are mechanically restrictive or rely on beat-to beat repeatability of cardiac motion that is practically difficult to achieve. Another approach utilized in present day scanners is the reconstruction of images at multiple phases in an attempt to select a volume reconstructed at the quiescent phase of the heart. However, the temporal resolution in currently available CT scanners does not suffice for motion free cardiac imaging of all coronary segments at higher heart rates or highly variable heart rates. Certain other techniques, not commercially available but under investigation, relate to model-based estimation requiring reconstructions of several cardiac phases to estimate the motion. Such techniques require longer X-ray exposure time and involve a number of computational challenges.
It may therefore be desirable to develop an efficient technique to improve resolution of acquired CT images by reducing motion induced blurring and other motion artifacts. Additionally, there is a need for a low cost technique that minimizes the amount of scan data required for motion estimation, thereby minimizing dose administered to a patient.